1. Field of the Invention
The present invention relates to a driving support system installed in various mobile objects such as a car and a motorcycle, and in particular, the invention relates to a display device suitable for a driving support system, a helmet provided with a display device, and a driving support system including a display device.
2. Description of the Related Art
In recent years, driving support systems for various mobile objects (car, motorcycle, plane, and the like) have been actively developed aiming for improvement of driving as to safety and comfort. ‘Adaptive Cruise Control System’ has already been produced by using a driving environment sensing technology, which is a driving support system for controlling the constant speed drive, for controlling car following the preceding vehicle (for controlling a distance between cars).
In addition, for example, disclosed in Patent Document 1 is a technology of detecting surrounding objects such as other vehicles and of giving a warning in the case where any obstruction is detected.
Furthermore, various kinds of car navigation systems have been put into practical use. Patent Document 2 is an example thereof. The route guidance is carried out by the car navigation system in the following manner. The car navigation system stores map data in a memory device thereof in advance and receives a detected signal from driving condition detecting sensors such as a direction sensor, an angular speed sensor, and a distance sensor or receives a location signal such as latitude and longitude data from a satellite by using a GPS. According to either or both of the detected signal and the location signal, the car navigation system measures the present location and reads out the map data from the memory device based on the result of measurement, so that the present location is displayed by a display device thereof.
The display device of the car navigation system is a liquid crystal display device, a display device using a CRT (cathode-ray tube) or the like, or a projection display device.
As the car navigation system is assumed to be installed in a vehicle, it is difficult to install the system in a vehicle having small frontspace around a driver's seat such as a motorcycle and a snowmobile. In addition, in the case where the display device is installed in the vehicle, it cannot be set within the forward sight of the driver. Therefore, the driver can not keep his eyes ahead at the wheel in order to view the display device and it is very dangerous. In view of this, it is proposed that a means for projecting data is provided in a helmet for a driver to project data within a sight of the driver as disclosed in Patent Document 3.
Disclosed in Patent Document 4 is a display system for adjusting luminance in accordance with surrounding circumstance data or living body information of a user of an EL display device.
Disclosed in Patent Document 5 is a game machine that works in accordance with the mental and physical conditions of a player by using a chaos attractor.    Patent Document 1: Japanese Patent Application Laid-Open No. Hei 6-215300    Patent Document 2: Japanese Patent Application Laid-Open No. Hei 6-88731    Patent Document 3: Japanese Patent Application Laid-Open No. Hei 5-85446    Patent Document 4: Japanese Patent Application Laid-Open No. 2001-272968    Patent Document 5: Japanese Patent Application Laid-Open No. Hei 6-182056
Since a display device of a driving support system is either a direct-view display device such as a liquid crystal display device and a display device using a CRT, or a projection display device, the display device is installed in or on a dashboard.
In the case where the direct-view display device is installed in the dashboard, a driver can not keep his eyes ahead at the wheel in order to view the display device and it is very dangerous.
In the case where the direct-view display device is installed on the dashboard, the display device itself blocks part of the forward sight of a driver.
On the other hand, in the case where the projection display device is installed in the dashboard, displayed data is displayed forward at a windshield as a virtual image. Therefore, a visual image superposed the displayed data on a front scene is displayed, so that safe driving is realized. However, it is difficult to design an optical system due to a curve of the windshield. Further, it is extremely difficult to design an optical system for such a precise display as a map. Since the projection display device also requires a strong light source, the power consumption becomes quite large and large load may be applied to a battery of a mobile object. In addition, the projection display device requires a light path for projection, which is difficult to be provided in a limited space inside vehicle even when a mirror and the like are used. The projection display device is also difficult to be viewed by a person in a passenger seat other than a driver due to its narrow viewing angle.
It is preferable that a display device can be installed easily. Since the projection display device is installed in a dashboard, it takes some trouble to repair it when it breaks down. Besides, when the display device is under repair, a car cannot be used even when there is nothing wrong with the car.